More Solar Hot Water

Solar Hot Water - How it works

On the right is a simplified diagram of an Active Closed loop system. When there is sufficient heat to be drawn from the collectors (A), the controller (B) automatically activates the pump(s). The heat transfer fluid (HTF) is then circulated from the collectors, through the heat exchanger (B), where its heat is transferred to water in the storage tank (C). The HTF is then pumped back to the collectors to once again be reheated. This circulation loop will continue as long as there is heat to be drawn from the collectors. During times when there is little or no sun, a backup heating system will be activated to provide adequate hot water.

There are many variations on this simple system. Some use two AC pumps to circlulate the water and the HTF. Some use a single pump which can, optionally, be powered by a small PV panel instead of standard AC. Some drain the fluid out of the collector loop at night, and some use glycol (like antifreeze) in the collector loop to prevent freezing. The diagram below shows a typical closed-loop glycol system.